I cannot abide everyone agreeing, so I will offer an alternative reality :)
Clearly that trailer is not worth $7k, or even $3k, on the market. But the question should be, is it worth it to you? You apparently like the location, and you like the deck which adds value. And usually an existing deck would not work with a different trailer. So, how much is that camping site worth to you? Have you got $5k to throw at a weekend getaway site?
The salvage title isn't much concern if that trailer is never leaving that site. Won't see the road ever again. I don't see why insurance would be needed, unless it is a requirement of the property owners. And even if it is, it would not be expensive for some kind of liability coverage, which is all they can reasonably require. It's not like you need replacement coverage. Unless of course you have to finance this purchase, in which case this would be a foolish purchase.
So let's assume this trailer is going to sit there for the rest of its life. Let's further assume this life expectancy is 5 years. Then $5k will cost you $1k per year for a vacation site, plus whatever the site rental costs, and a little maintenance which any trailer would require. I dunno your situation, but $1k per year is pretty cheap. Figure at the end of whatever the life span ends up, you are going to walk away from this thing, because it will may have near zero value.
I don't know your financial position, but hopefully this is a vacation kind of deal, and not your future fulltime living arrangement.
I don't know about NC, but in CA, plenty of folks are driving vehicles with salvage titles, and buying insurance. No big deal, but it's a big hit at resale time. I don't see resale as any issue in this instance.
